Myth
There is no back arch on a kick serve and players should be taught to keep their back completely straight to prevent injury.
In addition, the toss should be in the same place as first serve to prevent back arch and to disguise the kick serve.
Truth
The lower spine should be kept straight to prevent injury.
The upper thoracic spine and cervical spine should arch to help accelerate the racquet and position the body underneath the ball with the chest opening underneath the ball.
All top pros extend the thoracic and cervical spine when hitting kick serves.
Moreover, most pros toss slightly more left and always closer to the body then on the first serve. John Yandell and I have demonstrated this time and again through high speed video analysis.
You simply cannot get the same action on the ball or the same angle out wide with a completely neutral toss or toss to the right.
The pros can still disguise the kick when tossing slightly left because they can still vary the location and delivery from that tossing spot.
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